Cellular differentiation will be studied in neural plate cells of the early chick embryo. Differentiation of neural cells will be identified by indirect immunofluorescence staining using cell-type-specific antibody probes for neurons, astrocytes, oligodendrocytes and fibroblasts. Studies will be carried out to locate precursor cells in neural plate and map regions which exhibit morphogenetic activity for parts of the neural system of the embryo. The "determined" state of neural plate cells will be altered by subjecting cells to various dissociation and grafting techniques. These investigations will test the stability of the "determined" state and examined the preceding events in its establishment. Other experiments will establish whether the neural plate is composed of subpopulations of committed cells of non-overlapping developmental fates or whether they are "pluripotent". The approach will be to isolate neural plate cells and transform the cells with a temperature-sensitive mutant of Rous sarcoma virus, tsNY68, to inhibit differentiation and then to utilize the property of transformation which allows cloning of individual cells. The tsNY68 transformants will be grown to large number and then shifted to the nonpermissive temperature to allow the clones to express their developmental potential. The long-range goal of this project is to analyze molecular mechanisms which regulate early neural differentiation. Such information will be of importance in understanding control mechanisms operating in malignancy.